The present invention relates to fiber optic cables and, more particularly, to fiber optic cables having at least one water blocking feature.
A fiber optic cable generally comprises a jacket, strength members, and one or more optical fibers disposed within the passageway of the jacket or within one or more buffer tubes disposed within the passageway. Fiber optic cables that are intended for outdoor or indoor/outdoor use generally also include elements for preventing or mitigating the effects of water that may infiltrate into the interior passageway(s) of the cable. In particular, it is undesirable to allow water to migrate longitudinally along the passageway(s) of the cable because the water may reach cable closures or connectors, which can be damaged by exposure to the water. Accordingly, many fiber optic cables include water blocking elements for preventing migration of water longitudinally along the cable interior.
A commonly used technique for preventing water migration through the cable is to fill the interior passageway(s) of the cable with a petroleum based grease-like compound. However, there are many disadvantages attendant to the use of such compounds. For this reason, xe2x80x9cdryxe2x80x9d fiber optic cables have been developed. A dry fiber optic cable typically includes a water swellable element that swells when exposed to water so as to form a blockage in the cable preventing water from flowing past the blockage. The water swellable element often comprises a superabsorbent polymer composition coated on or impregnated in a yarn or tape that is wrapped about the fiber(s) all along the length thereof.
Such water swellable yarns or tapes are effective in preventing water migration through a cable. A drawback of their use, however, is that they can restrict free movement of the fiber(s) within the cable passageway(s), which movement is desirable during thermal elongation or contraction of the cable. As a result, the water swellable yarns or tapes can affect the attenuation performance of the cable relative to that of a comparable grease-containing cable.
An aspect of the present invention comprises a fiber optic cable with a small outside diameter and a non-petroleum based water blocking zone, comprising a cable jacket, at least one optical fiber disposed within the cable jacket, with the water blocking zone at least partially filling the cable. The water blocking zone comprising a soft, solid material having a three-dimensional network of bonding, defining a multifunctional component. The water blocking zone provides water blocking, defines a buffer that allows desirable levels of optical fiber movement, and is operative to cushion mechanical loads. The water blocking zone preferably comprises a thermoplastic or thermoset material. The water blocking zone can comprise a foamed or non-foamed material.